A gender symbol can be one of the many symbols used to denote the gender of a life form.
Their Origins
All the gender symbols come from those of our Solar System's planets.
Standard Gender Symbols
From the symbol of Venus (Unicode: ♀). The symbol for a female organism.
From the symbol of Mars (Unicode: ♂). The symbol for a male organism.
From the symbol of Mercury (Unicode: ☿). The symbol for an intersexual or transgender organism.
From the symbol of Sagittarius (Unicode: ♐). The symbol for an unknown gendered organism.
From the symbol of Earth (Unicode: ♁). For generally everything of Earth; anonymous.
From the female and male symbols. Anonymous; intersexual or transgender.
Religious Gender Symbols
From the symbol of the Sun (Unicode: ☉). The symbol for the higher power in some practices.
From the symbol of Neptune (Unicode: ♆). The symbol for the embodiment of evil in some practices.